1. Field of the Invention
The present disclosure relates to a roller, a heating member, and an image heating apparatus equipped with the roller and the heating member, which are configured to heat an image on a sheet. The image heating apparatus is used in image forming apparatuses, such as a copying machine, a printer, a facsimile machine, and a multifunction peripheral equipped with a plurality of functions including copying, printing, and facsimile. Further, the present disclosure is directed to preventing or reducing a partial increase in temperature of a belt and to preventing or reducing a partial increase in temperature of a heating member.
2. Description of the Related Art
Image forming apparatuses, such as electrophotographic apparatuses and electrostatic recording apparatuses, are equipped with a fixing apparatus (image heating apparatus) as a unit for heating and fixing an image formed on a sheet. Also, in recent years, there have been proposed fixing apparatuses in which a heating element is provided in a fixing belt (heating rotary member) itself from the viewpoint of energy saving. Such fixing apparatuses, having a configuration with a low thermal capacity, do not require a long warming-up time and, therefore, can operate with reduced power.
In a fixing apparatus discussed in Japanese Patent application Laid-Open No. 2009-109997, an elastic roll is located inside a heating belt (heating rotary member) equipped with a resistance heat generation layer. This configuration enables a nip portion to be formed between the elastic roll and a pressure roll via the heating belt. In addition, Japanese Patent application Laid-Open No. 2009-109997 discusses such a configuration that the elastic roll is made of a foam material. This configuration enables a heat quantity of the resistance heat generation layer to be efficiently used for image fixation and thus can reduce a warming-up time.
However, the fixing apparatus discussed in Japanese Patent application Laid-Open No. 2009-109997 has an issue in that the use of a foam material for the elastic roll may decrease not only the thermal conductivity in a radial direction of the elastic roll but also the thermal conductivity in an axial direction thereof. In other words, in a case where the fixing apparatus continuously performs a fixing process using sheets with a size narrower than the width of the heating belt, regions of the heating belt outside the sheet width in the width direction may increase in temperature. Therefore, it is desirable that the fixing apparatus is configured to have a uniform thermal effect with the improved thermal conductivity in the axial direction of the elastic roll to reduce an increase in temperature of the above-mentioned regions.